The present invention relates to an antenna for a radio communications apparatus operating in the frequency range of 800 MHz-3 GHz with a first radiating element in the form of a slot in a substantially planar foil or disc-shaped metal conductor, and a second radiating element set to a different resonance frequency from the first element.
In the employment of mobile radio communications apparatuses, in daily parlance mobile telephones in an urban environment, problems are often encountered in transmission and receiving. The reason for this is that, in such an environment, there are often dead zones which cannot be reached in communication with a certain cell in the system.
In order to remedy this problem, use is often made of duplicated antennae in mobile telephones, these antennae having different directive effect, polarisation and/or appearance on the antenna lobe. Such a second antenna is often entitled a diversity antenna.
Swedish Patent Application No. 9701646-3 describes a diversity antenna which is designed as a double so-called F-antenna (often called a notch antenna, slot antenna or slit antenna). The pertinent antenna includes a double-sided, L-shaped circuit card where the radiating slots are disposed in the metallic conductor layers disposed on the opposing sides of the circuit card. The slots have meandering formation so as to reduce the physical construction size of the antenna. Further, both of the slots are set to different resonance frequencies.
The antenna construction described in Swedish Patent Application No. 9701646-3 is intended for integration in a so-called mobile telephone. Here, the manifest trend moves towards smaller physical dimensions, from which it follows that the space for the antenna will be less and less, the further this development trend moves.
Because of the slight space available, it often happens that the antenna will be placed immediately outside and more or less parallel with a metal plane. The metal plane may consist of a carrying metal body which imparts firmness to the chassis of the telephone, of a screen plate or of the earth plane in an electronic card. By coupling and reflection, the properties of the antenna are greatly influenced if it is placed too close to such a metal plane. The free radiation is affected, as well as other properties such as, for example, impedance adaptation between antenna input and antenna cable across the antenna""s working frequency range and the antenna""s degree of efficiency, etc.
The above described problems begin to become considerable when the distance between the antenna and the metal surface approaches a tenth of a wavelength. In shorter distances, the function of the antenna increasingly deteriorates in order subsequently to be no longer acceptable.
The present invention has for its object to design the antenna disclosed by way of introduction such that it will be suited for use even in extremely cramped spaces. Thus, the present invention has for its object to design the antenna such that, with retained good function and high degree of efficiency, it may be placed extremely close to a metal plane disposed in a radio communications apparatus. The present invention further has for its object to design the antenna such that it will have good directive effect, good efficiency and above all extremely small dimensions, as well as good band width capability.
The objects forming the basis of the present invention will be attained if the antenna intimated by way of introduction is characterized in that the metallic conductor is placed close to a second conductor in the form of a metallic surface, and that the second radiating element is formed from an edge portion of the first conductor or a gap or an interstice between this edge portion and the second conductor.
Further advantages will be attained if the antenna is also given one or more of the characterizing features as set forth in appended claims 2 to 13.